1. Field of the Invention
The present invention relates to the field of design and construction of bicycles. More particularly, the present invention relates to the field of design and construction of the suspension forks for bicycles.
2. Description of the Prior Art
Various suspension forks for bicycles have been introduced in the prior art. The following three (3) patents are found to be pertinent:
U.S. Pat. No. 4,971,344 issued to Turner on Nov. 20, 1990 for "Bicycle with A Front Fork Wheel Suspension" ("the Turner Patent").
U.S. Pat. No. 5,060,961 issued to Bontrager On Oct. 29, 1991 ("the Bontrager Patent").
U.S. Pat. No. 5,193,832 issued to Wilson et al. on Mar. 16, 1993 for "Suspension for Bicycles" ("the Wilson Patent").
The Turner Patent discloses a front fork wheel suspension for a bicycle. The front fork suspension of the Turner Patent provides two improvements to a bicycle front fork having two telescoping suspension assemblies. The first improvement includes a fluid containing circuit for each of the telescoping suspension assemblies, where the fluid containing circuit is designed not to absorb pedal driven energy, but rather to absorb only impact shocks imposed upon the front fork.
There are several disadvantages of this fluid containing design. First, fluid-containing suspension systems generally are not as reliable and durable as no-fluid suspension systems for various reasons, such as the variation of the viscosity of the fluid due to drastic temperature changes, or the leaking of the fluid resulting from the aging of the sealing materials. Second, the Turner Patent fluid-containing bicycle fork has a completely closed assemblement, which means that a rider cannot readily adjust the damping effect of the suspension systems. Third, the complicated structure of the fluid-containing telescoping assemblies makes it very difficult to maintain and repair.
The second improvement of the Turner Patent includes a cross member interconnecting the respective top parts of the two lower tubes of the two telescoping suspension assemblies, where a wheel rim brake is carried by the lower tubes at the location where the cross member connects. This design provides a means for preventing the two legs of the bicycle fork from twisting and rotation, and from moving independently. However, the disadvantage of this design is that it puts all the stresses at the top end of the lower leg, including the bending stress between the upper leg and the lower leg, the twisting stress from the other leg transmitted through the cross member, and the braking force transmitted from the brake post which carries the rim brake.
The Bontrager Patent discloses a bicycle front fork crown assembly. The front fork crown assembly includes a crown, a steerer and two blades. The steerer and the two blades are interconnected by the crown. The crown disclosed by the Bontrager Patent is a unitary piece having a central steerer bore hole and two opposite blade bore holes. All three bore holes are intersected by respective engagement slots. Although the detailed embodiments of the Bontrager Patent are slightly different, they all have the common feature of having the steerer bore hole intersected by an engagement slot.
The disadvantage of having an intersecting slot in the middle of the bicycle crown is that it significantly reduces the strength of the crown. In addition, fastening the steerer to the crown by bolts increases the chance of losing control over the front wheel when the bolts are loosened.
The Wilson Patent discloses a shock absorbing suspension system for a bicycle front fork. The shock absorbing suspension system includes a tube, a strut slidable in the tube, a member connecting both tubes to the handlebars, a biasing member between the tubes and the struts, a rim actuating braking mechanism, and a by-pass connection connecting the braking mechanism to each of the struts. The skewered elastomer bumpers of the Wilson Patent are located inside the top portion of the tubes which are the upper legs of the bicycle front fork. This design makes it possible for a rider to have easy access to the elastomers through the top open end of the tube, so that the rider can replace or exchange the elastomers to adjust the damping effect of the fork, which is very desirable.
In order to achieve this "top-accessible" arrangement, the design of the Wilson Patent has two arrangements. First, the skewered elastomers are placed between the tube and the strut so that the elastomers can resist the strut to slide into the tube and urge the strut to slide out of the tube, thereby providing a damping effect. Second, a by-pass connection is utilized to by-pass the tube and connect the rim brake to the strut, because the rim brake has to be connected to the strut (the lower end of which is fixed to the front wheel axle) to ensure that the distance from the front wheel axle to the rim brake is maintained at a constant distance.
However, each of these two arrangements has its disadvantages. The disadvantage of having the elastomers placed between the tube and the strut is that the elastomers can only damp the strut when it slides into the tube, but provides no damping when the strut slides out of the tube. In other words, the elastomers have no restraint on the strut when it is sliding out of the tube from its balanced position. Therefore, the design of the Wilson Patent provides no rebound damping or rebound control.
In addition, the disadvantage of using a by-pass connection for connecting the rim brake to the strut violates the integrity of the bicycle fork. In one embodiment of the Wilson Patent, the by-pass connection includes a slot on the sidewall of each tube for allowing the braking mechanism to be mounted to the strut therethrough. This embodiment increases the possibility of dust or other dirt entering into the telescoping tube assemblies because there is an open slot on the outer tubes of the fork. In the alternative embodiment of the Wilson Patent, the by-pass connection includes two collars slidably mounted on each tube for attaching the braking mechanism, and connected by a tie rod which in turn is attached to the axle of the front wheel. This embodiment is seriously flawed because when a rider brakes, the collars are likely to be tightly engaged with the tubes because of the brake force and the twisting stress between the legs and the cross brace. However, since the collars are connected to the rigid tie rods which are in turn fixed to the wheel axle, the tight engagement of the collars and the tube will act to prevent the sliding movement between the strut and the tube, thereby seriously reducing the damping effect of the fork.
It is desirable to design and construct a new suspension fork for bicycles which can eliminate the above-mentioned disadvantages in the prior art, while still providing the rider with all the desired features.